The invention relates to a synthesis method of an ultraviolet fluorescent molecular probe 3-dimethylamino phenyl-4-amino-N-butyl-1,8-naphthalic acid imine and an application of the ultraviolet fluorescent molecular probe in detection of nitrite of various actual samples. The ultraviolet fluorescent probe 3-dimethylamino phenyl-4-amino-N-butyl-1,8-naphthalic acid imine with specific recognition performance on the nitrite is synthesized by employing naphthalimide as a skeleton and N,N-dimethyl phenyl as a specific recognition group; and the ultraviolet fluorescent probe has the characteristics of being stable in optical property, good in specificity, high in sensitivity, short in response time, easy to prepare and low in cost. The content of the nitrite in various actual samples is determined by using 3-dimethylamino phenyl-4-amino-N-butyl-1,8-naphthalic acid imine; the content of nitrite in the samples is determined through an ultraviolet fluorescence spectrum; and meanwhile, whether the samples contain the nitrite or not is qualitatively judged through a color change. 3-dimethylamino phenyl-4-amino-N-butyl-1,8-naphthalic acid imine has the ability of quickly and conveniently detecting the nitrite.